Collocated wireless coverage areas using different channels can still interfere with each other, adjacent channel suppression depends largely on the receiver implementation and transmitted spectral mask. Similarly, overlapping or adjacent wireless LAN coverage areas using uncoordinated spread spectrum mechanisms such as direct sequence or frequency hop spread spectrum also “intentionally” interfere with each other to a certain extent when the same or adjacent channels are used at the same time. Typically these channels are defined by frequency, (as used in frequency division multiple access) time slot (time division multiple access), code (code division multiple access) or a combination. The level of interference on a given channel will depend on many factors including the signal strength of the wanted and interfering signals which in turn will depend on their transmission power level and the signal propagation environment, for example whether there is likely to be a strong multipath fading of the wanted or interfering signal as is typically difficult to predict in indoor environments.
The level of interference which is acceptable can also depend on what type of data is being transmitted. For example non-real time data such as email can be re-transmitted if not received correctly. However other types of real time data such as video base layer frames are more critical and sensitive to delays such as re-transmissions and therefore require a higher quality channel to deliver them in good time.
“Dynamic Reconfiguration and Efficient Resource Allocation for Indoor Broadband Wireless Networks” by Tim Farnham and Brian Foxon, Universal Personal Communications, 1998, ICUPC'98, IEEE 1998 International Conference, Vol 1, 1998, pages 53-57; describes an indoor radio access network having clusters of access points or base stations that use a combination of time division and frequency division multiple access mechanisms. The network sets different interference thresholds for type 1 (video) and type 2 (data) traffic, the type 1 threshold being lower as video is delay sensitive which means it needs to be sent first and accurately to avoid the need for re-transmission. The network switches between different channels when too many type 1 packets are waiting for transmission through an existing channel because its interference level is too high. The trigger for a channel change is based on the average buffer occupancy and error rate over time.